Unlike your wrist bones, a bird has a half-moon-shaped bone that allows this motion.

Click on the wrist joint for a closer look.

That half-moon-shaped bone, called the semilunate bone, is shown here in red.

Not all ancestral species had a semilunate bone, as you might remember from an earlier lesson.

Map where the semilunate bone evolved.

Oops.

Look carefully at where the semilunate wrist bone appears on the lineage, and try again.

Both Velociraptor and Archaeopteryx had a semilunate bone, so that feature must have appeared in their most recent common ancestor.

Now that we have mapped three traits that affect how well a bird can fly, let's review what we have just learned about flight and the importance of these features.